Pitch control in paper mill systems

Abstract: Pitch in paper mills is controlled by treating these systems with a water soluble polymer which contains a lower alkyl N-vinyl amide or a hydrolyzed lower alkyl N-vinyl amide polymer.

Description: FIELD OF THE INVENTION The invention relates to the use of certain N-vinyl amide polymers for use in controlling pitch in paper mill systems. INTRODUCTION The problem of pitch control in papermaking has previously been recognized. The pitch in the fibers of wood pulps is associated with naturally occurring lignin dispersing agents. Cooking and mechanical agitation which occur during the pulping by the sulfite process liberate pitch and these natural dispersing agents. But, as a result of the mechanical work on the fibers, the natural dispersing agents liberated along with the pitch are inadequate to keep the pitch from depositing on the equipment employed in beating, hydrating, refining, bleaching, and even on the wire used for forming the sheet. Because of the tendency of the pitch to agglomerate within the pulp suspension or deposit on the surfaces of the wire or other equipment, the pitch frequently causes the formation of spots or holes in the sheet formed or may adhere to the wire or press rolls or drier rolls and cause tearing of the sheet. This results in the production of sheets with numerous imperfections. Among other consequences involved are the expense of cleaning the machinery frequently either with solvents or steam, and the loss of production during cleaning and during replacing operations caused by breakdown of the sheet. Cationic water soluble polymers are used commercially in the paper mills as pitch control agents. The present invention is predicated upon the discovery that certain water soluble lower alkyl N-vinyl amide polymers give colloidal pitch particle reduction in aqueous pulps. THE INVENTION The invention refers to the use of a specific water soluble polymer for controlling pitch deposition in pulp and papermaking systems as defined in claims 1 to 6. It comprises adding to the pulp a specific amount of a water soluble polymer which contains at least 5 mole percent of a lower alkyl N-vinyl amide or hydrolized lower alkyl N-vinyl amides. The lower alkyl N-vinyl amide polymers and the hydrolized lower alkyl N-vinyl amide polymers for use in the practice of the invention have average molecular weights within the range of between 10,000 and 500,000. THE LOWER ALKYL N-VINYL AMIDE POLYMERS The polymers used in the practice of the invention contain at least 5 mole percent of the lower alkyl N-vinyl amide. In most instances the amount of the lower alkyl N-vinyl amide present in the polymer will be greater than 25 mole percent. The lower alkyl group of the N-vinyl amide usually contains from one to three carbon atoms. Illustrative of the lower alkyl N-vinyl amides that are present in the polymers used in the practice of the invention are N-vinyl acetamide and N-methyl(N-vinyl acetamide). The other monomers present in the lower alkyl N-vinyl amide polymers may be selected from such monomeric groupings as N-vinyl amine, vinyl glycine, vinyl acetate, vinyl alcohol acrylic acid, acrylamide and N-vinyl amides having an alkyl group containing between 12-22 carbon atoms. The amount of comonomer or termonomer present in the polymers of the invention often will be controlled by the method of preparation and the effectiveness of a particular polymer in the control of pitch in a particular papermaking system. The preparation of these polymers is frequently accomplished by the hydrolysis of a precursor lower alkyl N-vinyl amide polymer. Depending upon the degree of hydrolysis the resulting polymer is either a polyvinyl amine (full or complete hydrolysis) or a polyvinyl amine copolymer of the starting lower alkyl N-vinyl amidewhich results from partial hydrolysis. Polymers containing vinyl alcohol groups are produced by the hydrolysis of lower alkyl N-vinyl amide-vinyl acetate copolymers. This hydrolysis often results in the production of vinyl amine groups as well as vinyl alcohol groups. Many of the lower alkyl N-vinyl amide copolymers are prepared using conventional polymerization techniques. Thus, the copolymers with acrylic acid or acrylamide are prepared in this fashion. These monomers typically are present in the copolymers in amounts ranging between 5 to 95 mole percent. It is also possible to modify the polymers using organic modifying compounds such as alkylating agents to react with the vinyl amine containing polymers to produce secondary and tertiary amino groups. Typical is the use of chloroacetic acid to insert N-vinyl glycine groups into the molecule. It is possible to insert fatty amide groups into the polymers by reacting N-vinyl amine groups with fatty acid chlorides which contain from 12-22 carbon atoms. Such a compound is oleyl chloride. To illustrate typical polymers used in the practice of the invention Table 1 is presented below: Polymer No. Polymer Chemistry MW A Hydrolyzed p(vinylacetamide/vinylamine) Copolymer: 80-95% vinyl acetamide 20-50% vinyl amine 60,000-150,000 B A modified with chloroacetate: 60,000-150,000 Mole % N-vinyl acetamide 80-95 N-vinyl amine 15-4 }20% of vinyl N-vinyl glycine 5-1} amine groups were modified with chloroacetate acid C A modified with oleyl chloride 60,000-150,000 Mole % N-vinyl acetamide 80-95 N-vinyl amine 17.5-2.5 N-vinyl oleamide 2.5 D Substantially hydrolized 1:1 p(vinyl acetate/N-methyl-N-vinyl acetamide) 10,200 In Table 1, the mole percents and the molecular weight ranges were furnished by the supplier of the N-vinyl amide or hydrolized N-vinyl amide. DOSAGE The Dosage and Utilization of the Polymers of the Invention The polymers of the present invention can be added to the pulp at any stage of the papermaking system. They usually can be added as an aqueous solution. The effective amount of these polymers to be added depends on a number of variables, including the pH of the system, hardness, temperature, and the pitch content of the pulp. Generally between 0.05 and 0.5 pound per ton of the composition is added based on the weight of the pulp slurry. The polymers of the instant invention are effective in controlling pitch deposition in papermaking systems, such as Kraft, acid sulfite, and mechanical pulp papermaking systems. For example, pitch deposition in the brown stock washer, screen room and decker systems in Kraft papermaking processes can be controlled. The term "papermaking" is meant to include all pulp processes. Generally, it is thought that the polymers can be utilized to prevent pitch deposition on all wetted surfaces from the pulp mill to the reel of the paper machine under a variety of pHs and conditions. More specifically, these polymers effectively decrease the deposition of metal soap and other resinous pitch components not only on the metal surfaces, but also on plastic and synthetic surfaces such as machine wires, felts, foils, uhle boxes and headbox components. EVALUATION OF THE INVENTION . Pitch Deposition Test Procedure It was found that pitch could be made to deposit from a 1.4% consistency hardwood kraft fiber slurry containing approximately 1,650 ppm of a laboratory pitch and approximately 300 ppm calcium hardness (as CaCo 3 ) by adjusting the slurry to the desired test pH (4.5 or 6.0), adding the appropriate amount of inhibitor chemical and mixing the fiber slurry in an Osterizer blender for 4 minutes. The deposit was determined by the difference between the starting weight of a Teflon coupon suspended into the slurry during the test, and the dried weight of the coupon plus deposited pitch after completion of the test. The laboratory pitch was comprised of a mixture of primarily resin acids, fatty acids, and fatty esters. Listed below are Tables 2 and 3 which show the polymers which were evaluated and demonstrated pitch control activity. INHIBITION OF PITCH DEPOSITION SOFTWOOD PITCH @ pH 4.5 POLYMER TABLE 1 DOSAGE ACTIVES LB/TON BASIS PITCH WEIGHT DEPOSIT (MG) % INHIBITION OF PITCH DEPOSITION Control-1 0.00 520 Control-2 0.00 489 Control-3 0.00 473 A 0.20 340 31 A 0.50 314 37 A 0.80 201 59 A 1.20 164 67 A 1.60 114 77 A 2.00 51 90 C 0.20 471 5 C 0.50 239 52 C 0.80 189 62 C 1.20 89 82 D 0.20 470 5 D 0.50 215 57 D 1.00 138 72 D 1.50 62 87 Control-4 0.00 497 B 0.50 524 -6 B 1.20 329 33 B 2.00 237 52 B 3.00 180 64 B 4.00 84 83 Control-5 0.00 492 Control-6 0.00 504 Average Control Pitch Deposit Weight = 495.8 1 Standard Deviation = 15.7 MG (3.2%) INHIBITION OF PITCH DEPOSITION SOFTWOOD PITCH @ pH 6.0 POLYMER TABLE 1 DOSAGE ACTIVES LB/TON BASIS PITCH WEIGHT DEPOSIT (MG) % INHIBITION OF PITCH DEPOSITION Control-1 0.00 610 Control-2 0.00 581 A 0.20 365 37 A 0.50 118 80 A 0.80 85 85 A 1.20 22 96 C 0.20 324 44 C 0.50 103 82 C 0.80 33 94 D 0.20 270 53 D 0.30 73 87 D 0.50 46 92 Control-3 0.00 581 B 0.20 529 18 B 0.50 366 37 B 1.20 116 80 B 1.80 77 87 Control-4 0.00 544 Average Control Pitch Deposit Weight = 579 1 Standard Deviation = 27.0 MG (4.7%)

Claims: Use of a water soluble polymer which contains at least 5 mole percent of a lower alkyl N-vinyl amide or a hydrolyzed lower alkyl N-vinyl amide and has an average molecular weight within the range of between 10 000 and 500 000 in a process for controlling pitch deposition in pulp and papermaking systems which comprises adding the polymer to the pulp at a dosage of between 0.02 - 0.2 kg (0.05 and 0.5 pound) per ton of the pulp slurry. The use of claim 1 where the lower alkyl N-vinyl amide is N-vinyl acetamide. The use of Claim 1 where the lower alkyl N-vinyl amide is N-methyl(N-vinyl acetamide). The use of Claims 1 to 3 where the lower alkyl N-vinyl amide polymer contains from 5 to 95 mole percent of at least one monomer from the group consisting of vinyl amine, vinyl glycine, an N-vinyl amide having an alkyl group of from 12 to 22 carbon atoms, vinyl acetate,vinyl alcohol, acrylic acid and acrylamide. The use of Claims 1 to 3 where the lower alkyl N-vinyl amide polymer is partially hydrolyzed. The use of Claims 1 to 3'where the hydrolized lower alkyl N-vinyl amide polymer is completely hydrolyzed.

Inventors: GREER CAROL S, REED PETER E, GREER, CAROL S., REED, PETER E.
Applicants: NALCO CHEMICAL CO, NALCO CHEMICAL COMPANY
Application year: 1994
Main classification: D21H21
IPC codes: D21H21, D21C9, D21H17